Electrical power circuits are used to convert standard alternating current (AC) service to a form usable by devices, and to regulate the amount of power provided in response to demand by electrical and electronic devices being powered by the power circuit. It is not uncommon for a device to be in a standby mode, where it is coupled to an AC source, but not operating in an active mode and providing power to some device or load (other than itself). It is common to leave electrical and electronic devices plugged into an AC source even while not in use so that the device is ready to operate. When plugged into an AC source the main power circuitry is powered. As a result, the device dissipates power at the main power converter circuitry.
Numerous examples of such devices exist, including, for example, televisions and other audio/visual equipment, appliances, and so on. One type of device that falls into this category is battery chargers. Many types of battery charges are designed to be left plugged into AC service so that a battery can simply be dropped into the charger and recharged without the user having to plug the charger into the AC source. For example, some organizations use communication devices to allow members to communicate with each other. Examples of such organizations include police, fire, and other public safety organizations. It is common for an organization member to place their communication device into a charger upon returning to an office or other facility. Accordingly, battery chargers commonly used by such organizations have multiple pockets to be able to receive multiple batteries or devices so that they can be charged at the same time.
A typical battery charger for rechargeable batteries that recharges battery at a rapid rate (typically about an hour for a fully discharged battery) contains a main power converter that converts the AC source power to a direct current (DC) level which is typically further regulated by a buck-type converter, as controlled by charge control circuitry which regulates current and voltage applied to the battery according to a charge regime which depends on the battery chemistry and desired rate of charge. The use of a buck regulator on the secondary side of the power supply to charge a battery has two functions. First, in multiple pocket chargers, where each pocket can be used to receive and charge a battery, each pocket can have its own dedicated buck regulator which is fed from the output of the main power converter. Furthermore, a buck regulator can prevent improper operation of the main power converter should the charging contacts be short circuited, as can happen accidently when some foreign object becomes placed in the pocket, or if the battery is defective.
However, when both a main power converter and a buck regulator are used, the inefficiencies of the two regulators are multiplied. Furthermore, in multi-pocket chargers, the main power converter has to be designed to support maximum electrical output when all pockets are charging, which typically means when only one pocket is being charged the main power converter is not operating at peak efficiency. During standby, even though the power converter is supplying less power, it typically has an even worse efficiency, which is why power adapters continue to dissipate considerable heat even in standby.
Therefore there exists a need for a power control circuit that addresses these and other issues associated with known power circuit configurations.